Social media services are web-based services that allow users to connect with each other and to share thoughts, photographs, videos, links, and other content with each other. For example, a user creates a viewable profile containing information related to the user. The user can upload a photograph and allow people connected with the user to view and comment upon the photograph. A user may also share a uniform resource locator (URL) link, which links to a news story or other web content that the user wishes to share with his or her contacts. The URL may link to a document stored online. For example, cloud storage services are web-based services that allow users to store word processing documents, spreadsheets, presentations, photographs, videos, and other files remotely. Users can access their files in the cloud storage service from any device that may connect to the cloud storage service. The cloud storage service may provide a URL for each file that a user stores in the cloud, and a user can share this URL with other people on a social media service.
When a URL is shared on a social media service, a thumbnail or snapshot of the URL target may also be posted along with the URL. This thumbnail gives other users a preview image of the content of the URL target. For example, a shared URL linking to a web page may include a thumbnail of a picture that is stored on the web page. If a web page is a news story, the picture may be a photograph associated with the news story. When a user shares a URL of a document stored on a cloud storage service, a thumbnail image of the document may also be posted. This thumbnail shows a preview of the document, for example the first slide of a presentation document. The cloud storage service may provide the social media service with a URL linking to the thumbnail so that it may be posted on the social media service. However, some cloud storage services may cache and update document thumbnails so that the most recent version of the document is always shown in the thumbnail. Thus if a user shared a document on a social media service and subsequently updated the document, the thumbnail of the document on the social media service is also updated to reflect the changes. This may cause problems if the user does not want others to see changes made to the document. In addition, if the document is deleted by the user, the social media service may still display a thumbnail of the document, thus allowing others to continue to view a preview of a document that has been deleted.